New script xcrypt.py: end-to-end encryption for IRC messages

End-to-end encryption plugin for WeeChat IRC messages using AES-256-GCM.

Features:
- AES-256-GCM authenticated encryption
- PBKDF2-SHA256 key derivation with 600,000 iterations (OWASP recommended)
- Automatic encryption/decryption of PRIVMSG messages
- Visual indicators (green "E>" prefix) for decrypted messages
- Per-nick and per-channel password management
- Secure password storage with master passphrase

Requires: cryptography library
Python: 3.8+

Documentation: https://anonshell.com/xcrypt/

Author: AnonShell